Repairing your van's drum brakes

Top tips to be able to confidently service and repair your van’s drum brakes.

Following on from last month’s wheel bearing service, this month, we’re looking at a caravan drum brake service and repair.

Often bearings and brakes will serviced at the same time (so it might be a good idea to reference last month’s Tech Talk column to service your bearings at the same time) but we wanted to focus on brakes this month to be able to expand on the subject.

On the van we’re looking at here, there was also some damage to the brake wires, so we’ll explain how to repair that should you strike similar trouble.

TIME TO LOOSEN UP

Start off by loosening the wheel nuts. Don’t remove them yet; the point of loosening them now is that it’ll be a lot harder to do so later when the wheels are off the ground.

Jack up the van and place on axle stands. Make sure that the stands are supporting the main chassis rails – you can use the jockey wheel to raise and support the front of the van. This is where you can do your first check to make sure that the van’s brakes are working. You’ll either need to hook up a battery to the brake wire and earth for the van’s brake circuit or – and this is a hell of a lot easier – plug your tow vehicle into the van. Get a helper to apply full van braking at the electric brake controller and see if you can spin the van’s wheels. The wheels should be locked solid.

Now the wheels can be removed, and it wouldn’t hurt to tuck them under the van while you’re working on it. It’ll reduce the chances of you tripping over them and gives you a back-up if the axle stands tip over. If you have decent axle stands with a wide footing, this should be a very unlikely scenario – but it pays to be cautious.

The next step is to take off the brake drum, first by removing the wheel bearing dust cap either by gripping it with a pair of pliers or gently tapping around its edges with a hammer. With the cap removed, you can take out the split pin (which locks the spindle nut in posi-tion).

Bend the single ends of the split pin until they’re as straight as you can get them. Then either tap out the pin from the single ends side with a hammer or grab a pair of pliers and pull it out from the looped end. Now get your trusty shifter or open-ended spanner and undo the spindle nut. The drum is now free to slide off the spindle but remember you’ve got a spindle washer and outer bearing loose in there so be prepared to grab them before they go rolling away on the floor.

SCORING TOP MARKS

Up next is a quick inspection of the brake and magnet surfaces. On the inside of the brake drum, what you’re firstly looking for is scoring marks or heavily worn surfaces on the inner circumference (if there’s more than 0.5mm wear). On the magnet-wearing surface of the drum you’re checking for bad score marks or uneven wear. If you find these problems you should replace the drums.

Now you can check the linings themselves for excess wear, contamination or damage. The linings should be replaced if there’s only 0.8mm material left on riveted linings or when they’re down to 1.5mm on bonded linings. Also check for oil contamination and for scoring marks – in both cases the linings should be binned and new ones fitted. If the leading and trailing edges of the linings are not bevelled, it’s a good idea to file a bevel into the edges. This is so that the linings are less likely to crumble or break off at the edges and do damage to the rest of the lining and brake drum.

Magnets typically wear unevenly, but if it’s at a sharp angle of wear of only about one-third of the width of the magnet then it needs to be replaced.

Now is a good time to check the brake wiring. This van had damaged offside brake wires we needed to fix. As there was plenty of slack in the wiring here, it was pretty straight-forward; we cut out the damaged section of wiring, paired back the insulation and soldered the wires together.

Make sure you heat up the soldering iron for a few minutes before using it. That’ll give you time to twist the wires together. Polarity is not important here, so it doesn’t matter which wires you pair to solder. Keep the soldering iron on the join until the solder has melted in. Then you can wrap electrical tape around the fresh join to avoid shorting the wires (or use heat-shrink tubing).

Now it’s time to start buttoning everything up. It’s a reverse of disassembly but you need to make sure you’ve tensioned the bearings by the right amount when you’ve refitted the spindle nut (and really, by rights, you should check the condition of the bearings while you’ve got the drums off). Tighten the nut until the brake drum becomes hard to spin. Then loosen the nut until you can spin the brake drum. It should be able to spin freely for a couple of revolutions before coming to a stop. Now you can fit the split pin and replace the dust cap.

Towards the bottom of the brake backing plate there’s a small rectangular hole that gives access to the brake adjuster wheel. Grab a screwdriver (or better still, a dedicated drum brake adjuster tool, as it’s a slightly different shape and much better suited to the job) and tighten up the brakes until the drum can’t move any more. Then back off the adjustment about seven clicks. Spin the brake drum – it should be able to do two revolutions on its own before slowly coming to a stop, if the adjustment is correct.

Refit the road wheel and tighten a few wheel nuts so that you can give the bearings a final check: Grab the wheel, one hand at the top, the other at the bottom and see if you can rock the wheel. If there is quite a bit of movement, you need to tighten the bearing up a bit, if there’s none or only a slight amount, you’re good to go with refitting all wheel nuts, dropping the wheels back onto the ground and torquing up the wheel nuts to 130Nm.